1. Field of the Invention
The present invention relates to an oxygen sensor for detecting the oxygen concentration in exhaust gas in an internal combustion engine, for example, or an oxygen sensor for detecting oxygen in a predetermined gas.
2. Description of the Related Art
In recent years, various oxygen sensors used for air fuel ratio control, etc., in internal combustion engines of automobile engines, etc., have been developed. Especially high-performance, long-life oxygen sensors for detecting the oxygen concentration in exhaust gas have also been finding increasing demand to cope with environmental protection problems of air pollution, etc., caused by exhaust gases.
For example, representative one of such oxygen sensors widely used has a structure wherein an oxygen sensing element formed like a hollow shaft closed at the tip made of an oxygen ion conductive solid electrolyte of ZrO2, etc., is housed in a cylindrical casing, the outer face of the tip of the oxygen sensing element is brought into contact with a detected atmosphere, and air as a reference gas is introduced into the space inside the oxygen sensing element for measuring the oxygen concentration in the detected atmosphere based on an oxygen concentration cell electromotive force occurring in the sensing element.
By the way, to install an oxygen sensor as described above in an automobile, the oxygen sensor often is attached to an exhaust pipe, etc., near a tire of the vehicle, for example, in addition to an engine room. In such a situation, the oxygen sensor is exposed to a considerable hostile environment in which it receives a jet of water drops at the rainy driving time, at the washing time, etc., dirt of oil, etc., is deposited on the oxygen sensor, or the oxygen sensor receives shock of jumped-up pebbles, etc. In this case, to protect the oxygen sensing element from water drop and dirt deposition, a highly strong and highly sealed structure as much as possible must be adopted as the structure of the casing housing the oxygen sensing element. However, air as the sensing element reference gas needs to be introduced into the casing and thus a communication section with the outside must always be provided. That is, to operate the oxygen sensor stably over a long term under a hostile environment, contradictory problems of enhancing fluid sealability of water, etc., at a given level or more and providing permeability need to be solved at the same time. To meet such a demand, for example, Japanese Patent Laid-Open No. Hei 8-201338 discloses an oxygen sensor of a structure wherein an air hole is made in a casing and is covered with a water repellent filter, whereby ventilation is allowed while the entry of water drops, etc., is blocked.
In the oxygen sensor, generally a ceramic separator is placed in the casing and leads from the oxygen sensing element or a heating element for heating the oxygen sensing element are passed through lead insertion holes as a structure for drawing out the leads from the casing. Such a ceramic separator prevents or suppresses a short circuit between the leads or terminals following the leads, for example. Each lead extends from a rear opening of the casing to the outside and the space between the lead and the opening is sealed by an elastic seal member of a rubber tap, etc., fitted into the opening. Normally, lead insertion holes made in the ceramic separator and the elastic seal member are formed so that their centers are arranged on a phantom circumferential path (pitch circle).
In the disclosed oxygen sensor, the leads are inserted into the elastic seal member and the ceramic separator at different pitch circle diameters and to absorb the pitch circle diameter differences, a comparatively large gap is formed between the elastic seal member and the ceramic separator. A ventilation structure consisting of an air hole and a water repellent filter for covering the air hole is provided corresponding to the gap position.
However, in the disclosed oxygen sensor, the ventilation structure containing the water repellent filter is formed corresponding to the gap between the elastic seal member and the ceramic separator, thus if a strong impulse force acts on the part, there is a possibility that the casing will be largely deformed at the position corresponding to the gap. In this case, it is feared that a cylindrical member fixing and sealing the filter from the outside, for example, by crimping may loosen because of the deformation of the casing, that the filter seal may be broken, and that water drops, etc., may bypass the filter and enter the casing through the air hole. Since nothing blocks the way of leaked water drops in the proximity of the air hole, the probability is also high that water drops will leak into the oxygen sensing element through a through hole, etc., made in the axial direction of the ceramic separator, for example.
It is an object of the invention to provide an oxygen sensor having a structure in which a seal of a filter forming a ventilation structure is hard to break although a predetermined gap is formed between an elastic seal member and a ceramic separator.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; and a cover member being placed coaxially with the casing so that an inside of the cover member communicates with the casing and coupled to the casing from an axial rear; wherein the cover member is placed so as to overlap the casing on an axial front of the cover member from an outside;
further wherein the overlap is formed with: a main crimp part being formed annularly in a circumferential direction of the cover member and the casing by crimping the cover member toward the casing; and a rotation prevention part for preventing the cover member and the casing from relatively rotating around the axis of the cover member and the casing in the annular main crimp part.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a ceramic separator being placed coaxially with the casing, supported directly or indirectly via a member in a casing support part formed at a rear end of the casing, and formed with a plurality of lead insertion holes axially penetrating the ceramic separator for inserting leads from the oxygen sensing element; a cover member being placed coaxially with the casing and coupled to the casing from a rear with the ceramic separator covered from an outside while allowing the leads to extend to the rear outside of the cover member; and a metal elastic member being placed at least between the cover member and the ceramic separator or between the casing support part and the ceramic separator in a compression state for producing a sandwich retaining force for the ceramic separator between the cover member and the casing support part.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a gas introduction structure having a filter holding part making a cylindrical form coaxial with the casing on a rear of the casing, having an inside communicating with the casing, and being formed in a wall with one or more gas introduction holes and a filter being placed so as to block the gas introduction hole or holes of the filter holding part for rejecting permeation of liquid and allowing gas to pass through, the gas introduction structure for introducing outside air into the casing through the filter and the gas introduction hole or holes; and a protective cover being formed like a cylinder for covering the gas introduction structure from an outside thereof for blocking or suppressing a direct jet of liquid drops to the filter or deposition of deposits of oil, dirt, etc., on the filter.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a gas introduction structure comprising a filter holding part making a cylindrical form almost coaxial with the casing on a rear of the casing, having an inside communicating with an inside of the casing, and being formed in a wall with one or more gas introduction holes, a filter being placed so as to block the gas introduction hole or holes on an outside of the filter holding part for rejecting permeation of liquid and allowing gas to pass through, and an auxiliary filter holding part being formed like a cylinder placed on an outside of the filter and formed in a wall with one or more auxiliary gas introduction holes for sandwiching the filter between the auxiliary filter holding part and the filter holding part, for introducing outside air into the casing through the auxiliary gas introduction hole, the filter, and the gas introduction hole; wherein the filter comes in intimate contact with an inner face of the auxiliary filter holding part at least in surroundings of the auxiliary gas introduction hole and a predetermined gap is formed between the outer face of the filter holding part and the filter at least in surroundings of the gas introduction hole.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a filter assembly being placed almost coaxially with the casing as a cylindrical body separate from the casing and coupled to the casing from a rear while allowing leads from the oxygen sensing element to extend to the rear outside of the filter assembly; and a coupling part for coupling the filter assembly and the casing, wherein the filter assembly comprises: a filter holding part making a cylindrical form almost coaxially coupled to the casing from a rear of the casing, having an inside communicating with an inside of the casing, and being formed in a wall with one or more gas introduction holes; a filter being placed so as to block the gas introduction hole or holes in the filter holding part from an inner or outer face side for rejecting permeation of liquid and allowing gas to pass through; and an auxiliary filter holding part for fixing the filter to the filter holding part, outside air introducing into the casing through the filter and the gas introduction hole.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a hollow shaft with a tip closed; a shaft-like heating element being placed in the hollow part of the oxygen sensing element for heating the oxygen sensing element; a cylindrical casing for housing the oxygen sensing element; and a ceramic separator being placed almost coaxially with a rear end of the oxygen sensing element and formed with a plurality of lead insertion holes axially penetrating the ceramic separator for inserting leads from the oxygen sensing element and the heating element; wherein the lead insertion holes are arranged so as to surround a center axis of the ceramic separator; the ceramic separator is formed with a heating element end housing hole opened at one end in the front end face of the ceramic separator with a bottom positioned in an axial intermediate part of the ceramic separator and an inner diameter set larger than an outer diameter of the heating element, the heating element end housing hole being formed by cutting away a center of the ceramic separator so as to overlap the separator lead insertion holes from the inside and the rear end part of the heating element being housed in the heating element end housing hole; and the heating element is offset so that a center axis thereof is one-sided with respect to a center axis of the hollow part of the oxygen sensing element in the proximity of a heating part of the heating element.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a ceramic separator being placed in the casing and formed with a plurality of lead insertion holes axially penetrating the ceramic separator for inserting leads from the oxygen sensing element; and an elastic seal member being coaxially integrated with a rear opening or a rear of the casing and having an inside fitted elastically into an inside of a different cylindrical body communicating with the casing and seal lead insertion holes for inserting the leads for sealing a gap between outer faces of the leads and an inner face of the casing or the different cylindrical body; wherein an axial rear end face of the ceramic separator adheres closely to an axial front end face of the elastic seal member, that the ceramic separator is formed with a ventilation communication part axially penetrating the ceramic separator, and that an opening of the ventilation communication part on a side near to the elastic seal member in the axial direction is made at a position where the opening is not shielded by the elastic seal member.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a gas introduction structure comprising a filter holding part making a cylindrical form almost coaxial with the casing on a rear of the casing, having an inside communicating with an inside of the casing, and being formed in a wall with one or more gas introduction holes, a filter being placed so as to block the gas introduction hole or holes on an outside of the filter holding part for rejecting permeation of liquid and allowing gas to pass through, and an auxiliary filter holding part being formed like a cylinder placed on an outside of the filter and formed in a wall with one or more auxiliary gas introduction holes for sandwiching the filter between the auxiliary filter holding part and the filter holding part, for introducing outside air into the casing through the auxiliary gas introduction hole, the filter, and the gas introduction hole; wherein the filter holding part has an axial front relative to a stepped part formed in an axial intermediate part of the filter holding part as a first portion and a rear as a second portion so that the second portion is made smaller in diameter than the first portion, the gas introduction hole being made in a wall of the second portion; the auxiliary filter holding part is placed so as to spread across the first and second portions of the filter holding part; a main coupling part for coupling the filter holding part and the auxiliary filter holding part to each other with the filter between is formed at a position corresponding to the second portion; and an auxiliary coupling part for coupling the filter holding part and the auxiliary filter holding part to each other is formed at a position corresponding to the first portion.
An oxygen sensor according to the present invention comprises: an oxygen sensing element shaped like a shaft; a cylindrical casing for housing the oxygen sensing element; a gas introduction structure having a filter holding part making a cylindrical form almost coaxial with the casing on a rear of the casing, having an inside communicating with an inside of the casing, and being formed in a wall with one or more gas introduction holes and a filter being placed so as to block the gas introduction hole or holes of the filter holding part for rejecting permeation of liquid and allowing gas to pass through, the gas introduction structure for introducing outside air into the casing through the filter and the gas introduction hole or holes; a ceramic separator being placed so that a rear thereof enters the inside of the filter holding part in an axial direction of the oxygen sensing element and a front enters the inside of the casing and formed with a plurality of lead insertion holes axially penetrating the ceramic separator for inserting leads from the oxygen sensing element; and an elastic seal member being fitted elastically into a rear opening of the filter holding part and having seal lead insertion holes for inserting the leads for sealing a gap between outer faces of the leads and an inner face of the filter holding part; wherein an rear end face of the ceramic separator is positioned on the rear side behind the gas introduction hole in the axial direction and a predetermined gap is formed between the elastic seal member and the ceramic separator at least at the lead insertion position.